This invention relates to an aircraft, and more particularly to a dual-mode aircraft being capable of operating in both a helicopter and fixed wing mode of flight.
The history of manned flight is replete with attempts to develop an aircraft capable of hovering like a helicopter, converting to a fixed wing aircraft, and cruising at high subsonic speeds. A successful, efficient design would have great utility because of its suitability for a large number of diverse missions, as well as its ability to take off and land from a very small, remote airfield. Past concepts of this type include the Herrick convertiplane, which used a rotating wing in autogyro mode for lift. This idea envisioned stopping and starting the main rotor using the energy available from the moving air as is the case with a traditional autogyro. It also had a fixed wing for additional lift during the conversion process. This concept was unable to hover or fly vertically because the rotor was not powered.
Another concept of this type, known as the Rotor/Wing (U.S. Pat. No. 3,327,969), was similar in that it was capable of hover, vertical and translational flight using a rotor consisting of a large centerbody with three stub blades. The powered rotor enable flight as a helicopter. The large centerbody was sized to provide the necessary lift during conversion to fixed-wing flight as the rotor slowed and stopped rotating. Once stopped and locked, the rotor became a wing. The sequence for conversion included pitching the aircraft nose down in helicopter flight while accelerating to conversion speed. Once this speed was achieved, the pilot pitched the aircraft nose up and entered autogyro mode. This provided an angle of attack necessary for the large centerbody to support the aircraft. At the speed in which all the lift was carried by the centerbody, the rotor was stopped and locked. The centerbody and stub blades then became a fixed wing. This concept heavily compromises the efficiency in helicopter mode due to the high induced power required with the stub blades and the efficiency in fixed-wing mode due to the large wing area associated with the large centerbody.
What is needed, therefore, is a dual mode aircraft which successfully combines the efficiency of a helicopter with the high-speed capability of a fixed wing aircraft, and is capable of smoothly, efficiently, and safely converting from one flight mode to another. The aircraft should be capable of hovering, vertical flight, and translational flight in an efficient manner.